Process for producing polyvinyl alcohol filaments

ABSTRACT

A PROCES FOR THE PRODUCING POLYVINYL ALCOHOL FILAMENTS OF CIRCULAR CROSS-SECTION EXCELLING IN DRAWABILITY WHICH COMPRISES USING AS A SPINNING SOLUTION AN AQUEOUS POLYVINYL ALCOHOL SOLUTION OF 10-30 WEIGHT PERCENT CONCENTRATION CONTAINING 1-5 WEIGHT PERCENT, BASED ON THE POLYVINYL ALCOHOL, OF A WATER-SOLUBLE BORIC ACID COMPOUND, THE PH OF SAID SOLUTION BEING ADJUSTED TO 3-5, AND SPINNING SAID AQUEOUS POLYVINYL ALCOHOL SOLUTION FROM CIRULAR SPINNING HOLES INTO AN AQUEOUS COAGULAING BATH CONTAININ 20-100 GRAMS PER LITER OF AN ALKALI HYDROXIDE AND 100- 180 GRAMS PER LITER OF SODIUM SULFATE, THE PH OF SAID BATH BEING ADJUSTED TO 13.5-14.

United States Patent US. Cl. 264-185 Claims ABSTRACT OF THE DISCLOSURE A process for producing polyvinyl alcohol filaments of circular cross-section excelling in drawability WlllCh comprises using as a spinning solution an aqueous polyvinyl alcohol solution of -30 weight percent concentration containing 1-5 weight percent, based on the polyvinyl alcohol, of a water-soluble boric acid compound, the pH of said solution being adjusted to 3-5, and spinning said aqueous polyvinyl alcohol solution from circular spinning holes into an aqueous coagulating bath containing -100 grams per liter of an alkali hydroxide and 100-180 grams per liter of sodium sulfate, the pH of said bath being adjusted to 13.5-14.

This invention relates to a process for producing polyvinyl alcohol filaments and, in particular, to a process for producing polyvinyl alcohol (hereinafter abbreviated to PVA) filaments having a circular cross-section true to the shape of the spinning hole and of a homogeneous and compact structure, which moreover excel in drawability.

With a view to obtaining hollow or transparent PVA filaments, it has been known to spin an aqueous PVA solution containing a water-soluble boric acid compound in an amount of 1 weight percent, at most based on the PVA, into an aqueous coagulating bath containing predominantly sodium or ammonium sulfate and adjusted to an alkaline state of a pH of the order of 8-9 with a small quantity of sodium hydroxide, ammonia or ammonium borate. However, in these methods, due to the fact that the content of the boric acid compound of the aqueous PVA solution was small and the pH of the aqueous coagulating bath was near neutral, the solidification of the freshly spun filaments was not onlyslow but also the resulting filaments did not have a cross-sectional configuration which was true to the shape of the spinning hole nor was the structure of the filaments sufficiently compact.

The object of the present invention therefore resides in providing a process for producing PVA filaments which do not possess the above-described shortcomings, this being accomplished by increasing the content in the aqueous PVA solution of the boric acid compound and by using a strongly alkaline aqueous coagulating bath.

According to our experiments we found that when an aqueous PVA solution containing a relatively large amount of a boric acid compound, as 1-5 weight percent, is extruded into a strongly alkaline aqueous coagulating bath containing a large quantity of an alkali hydroxide, the spinning could not be accomplished because of the abnormal high speed of coagulation. This is believed to be due to the fact that the large quantity of the boric acid compound contained in the aqueous PVA solution sets up a cross-linking reaction with the PVA under strongly alkaline conditions. As a result of a comprehensive consideration of these facts, we found that for achieving the foregoing object of the present invention by spinning an aqueous PVA solution containing a relatively large amount of the boric acid compound it was necessary to 3,660,556 Patented May 2, 1972 use an aqueous coagulating bath composed of a large quantity of an alkali hydroxide (this is an important condition for obtaining filaments having a compact structure and a cross-sectional configuration true to the shape of the spinning hole) along with a large quantity of sodium sulfate (this in an important condition for obtaining good spinnability).

That is to say, according to the present invention, PVA filaments of circular crosssection and homogeneous and compact structure can be obtained by spinning an aqueous PVA solution of 10-30 weight percent concentration whose pH has been adjusted to 3-5 and containing 1-5 weight percent, based on the PVA, of a water-soluble boric acid compound, from circular spinning holes into an aqueous coagulating bath containing 20-100 grams per liter of an alkali hydroxide and -180 grams per liter of sodium sulfate, whose pH has been adjusted to 1155-14. The so obtained filaments not only excel in drawability but also are without any nonuniformity in any of their properties at any portion longitudinally of the filaments, and moreover have an excellent touch and luster.

The aqueous PVA solution of a concentration of 10-30 weight percent to be used for spinning in the present invention must be, as hereinbefore noted, one containing 1-5 weight percent and preferably 2-3 weight percent, based on the PVA, of a water-soluble boric acid com pound and whose pH is moreover 3-5. As the boric acid compounds, included are such, for example, as boric acid and the water-soluble boric acid salts as sodium borate, potassium borate, ammonium borate and lithium borate. When the amount based on the PVA of these boric acid compounds is less than 1 weight percent, the coagulation speed is too slow, with the consequence that adhesion takes place between the freshly spun filaments. On the other hand, when the amount is greater than 5 weight percent, the coagulation speed is too fast, and in consequence breakage of the filaments immediately subsequent to their extrusion tends to take place. The adjustment of the pH of the aqueous PVA solution is carried out in customary manner by adding a minute quantity of a mineral acid such, for example, as sulfuric acid, hydrochloric acid or nitric acid. When the pH of the aqueous PVA solution is less than 3, the problem of the corrosion of the equipment arises on account of the excess acidity as well as the shortcoming which results from the coagulation speed being too slow. On the other hand, when the pH exceeds 5, the aqueous PVA solution becomes unstable, and the spinnability becomes poor because of too fast a coagulation speed. When the PVA concentration of the aqueous PVA solution is less than 10 weight percent, its coagulability is low and only filaments of low tenacity which are susceptible to breakage can be obtained, whereas when the PVA concentration exceeds 30 weight percent, the viscosity is too high and spinning is made difficult. The preferred PVA concentration of an aqueous PVA solution to be used for spinning filaments ranges from 14 to 20 weight percent.

According to the present invention, an aqueous PVA solution such as hereinbefore described is spun at a temperature of 20-40" C. in accordance with the customary PVA wet-spinning technique from circular spinning holes into an aqueous coagulating bath containing 20-100 grams per liter of an alkali hydroxide and 100-180 grams per liter of sodium sulfate, whose pH has been adjusted to 13.5-14. Thus the swelling of the filaments in the aqueous coagulating bath is prevented and filaments having a circular cross-section and of homogeneous and compact structure are formed. When the concentration of the alkali hydroxide is less than 20 grams per liter the coagulation speed is slow, with the consequence that the crosssectional configuration of the spun filaments does'not become round but becomes flat. On the other hand, when the concentration of the alkali hydroxide exceeds 100 grams per liter, an extreme decline in the spinnability occurs. The preferred concentration of the alkali hydroxide ranges from 40-80 grams per liter. Sodium hydroxide or 4 As regards the filaments of Controls 1 and 2, they were not circular in cross-section but were of cocoon shape and, in addition, they were of dual structure, being made up of skin and core portions. On the other hand,

potassium hydroxide, and especially the former, is suitable 5 the filaments of Examples 1-4 had a circular cross-secas the alkali hydroxide. When the sodium sulfate is used tion and, as can be seen from Table I, had a great critical in an amount less than 100 grams per liter, the spindraw ratio, in addition to excelling in their tenacity and ability declines and spinning either becomes totally imposresistance to hot water. sible or barely possible only when the spinning speed has been greatly retarded. On the other hand, when the EXAMPLE 5 amount of sodium sulfate exceeds 180 grams per liter, grams Weight Pefcfillt based on the of the dehydration speed becomes too fast so that instead of hori? acid was added to 830 f Water, the P 0f the being an advantage the formation of filaments having a $h1t1911 being ih f 4 y the addition of a minute circular cross-section becomes difficult, and filaments havquahtlty of Sulfur 1C acld- A 17 Weight Percent aqueous ing a flat or cocoon-shaped cross-section are formed as in Solutlon of PVA Was P P y addlhg 170 grams of the case where the spinning has been carried out by ex- PVA of h degree of Polymenzation 1700 and degree trusion of the PVA solution into a conventional aqueous of sifponlficatioh of 11101 Percent to this aqueous coagulating bath consisting predominantly of sodium sulfate or sodium carbonate. The preferred concentration of This aqueous PVA sohltlon Was p t an extrusion sodium sulfate ranges between 120 and 150 grams per liter. 20 rate 955 grams P mlmlte from a splmleret havlng The fil t Spun into an aqueous coagulating b h 300 clrcular holes each 0.11 mm. in diameter, into an according to the invention process are then taken out and q coagulatlhg bath Contalnlng 76 grams P h submitted to such after-treatments as neutralization, drawof sodlum hydroxlde and 122 grams P lltel' of Sodium ing and heat treatment thereby imparting to the filaments Sulfate, and adjl1ted to 3 P of The freshly Spun the various properties which they must possess to be of filaments were f from the bath t a P F of practical use. These after treatments may be carried out in 10 me ers per rulrlute, drawn 100%, neutralized w1th an customary manner. This is because the feature of the presaqueous heutrallllng hath Contalnlng grams P hter ent invention resides in the point that an aqueous PVA 0f Sulfllflc acld d 300 grams per hter of sodlum sulsolution of specified composition and pH is spun into an fate then Suhmltted t-heat drawlng of 1 00% folaqueous coagulating bath of specified composition and pH, lowed y watfir-washlng a d thereafter submitted drybut otherwise the operating conditions and apparatus used heat f of 300% to Obtam filaments having a total heretofore in the wet-spinning of PVA can all be applied draw of with no change whatsoever The so obtained filaments had a circular cross-section The invention will be illustrated more ifi ll by true to the shape of the spmmng holes and their structure the following examples and controls, it being understood homogemious- The tenaclty grams Per that these are not to be construed as limiting the invem denier, elongation was 5.5% and resistance to hot water tion in any manner whatsoever. was

CONTROL 4 EXAMPLES 14 AND CONTROLS 1-3 The aqueous PVA solution as used in Example 1 was Boric acid in an amount indicated in Table I was added Spun under identical. conditions as .infficated therein ipto and dissolved in 18 weight percent aqueous solution of an aquFous coagutatmg bath contammg 2 grams Per 1.1ter PVA having a degree of polymerization of 1700 and a of sodium hydrox1de and 250 grams per hter of sodium degree of saponification of 99.5 mole percent. The pH of Sulfate of P The freshly Spun filaments were this solution was then adjusted to the value indicated in drawn 100/0 'l rollers neutralized then Submmed.m Table I with a minute quantity of sulfuric acid. This aque- Wet'heat drawmg 100% followed by yater'washmg ous PVA solution was spun from circular spinning holes and thtafreafler submlttqd to dry'heat drawing of 200% into an aqueous coagulating bath of the composition and to obtam filamglts havmg a total draw ratlo of pH indicated in Table I. The freshly spun filaments were The obtatned filametlts had an oval cross'sectlon drawn 100% with rollers and then neutralized in a neuand tenaglty and resistance to q Water were tralizing bath containing grams per liter of sulfuric acid a per duper i 102 respectively both values and 300 grams per liter of Sodium Sulfate. This was {0L being greatly 1nfer1or to those of the filaments of Examlowed by submitting the filaments to wet-heat drawing of P16 100%, water-washing and dry-heat drawing of 225% to EXAMPLE 6 obtain filaments whose total draw ratio was 1200%. The 55 To 1000 grams of 20 weight percent aqueous PVA properties of the so obtained filaments are shown in solution containing 200 grams of PVA of a degree of Table I. polymerization of 1700 and a degree of saponification of TABLE I Properties 01 the filaments of total Aqueous coagulating bath draw ratio 1,200% Amount of boric acid pH of Composition (g.ll.) Resistance Critical based on aqueous to hot draw PVA (wt. PV Sodium Sodium Denier Tenacity Elongation water 1 ratio Experiment No. percent) solution hydroxide sulfate pH Number (gJdenier) (percent) 0.) (percent) t Resistance to hot water denotes the melt-breakage temperature of the filaments in pressurized hot water.

2 Could not be measured, since spinning was not possible.

99.5 mol percent was added 8 grams (4 weight percent based on the PVA) of boric acid, after which the pH of the aqueous solution Was adjusted to 3.1 by adding one gram of sulfuric acid. This aqueous PVA solution was spun from a spinneret as described in Example 5, into an aqueous coagulating bath containing 23 grams per liter of sodium hydroxide and 145 grams per liter of sodium sulfate, and adjusted to a pH 13.8. The freshly spun filaments were drawn 100% with rollers, neutralized, then submitted to wet-heat drawing of 100%, waterwashed and thereafter submitted to dry-heat drawing of 200% to obtain filaments having a total draw ratio of 1100%.

The cross-section of the so obtained filaments were circular, and they had a homogeneous structure. The tenacity was 12.3 grams per denier, resistance to hot water was 118 C. and critical draw ratio was 1900%.

CONTROL 5 Example 6 was repeated except that the aqueous coof the aqueous solution to 3. This aqueous solution was spun from a spinneret of the type used in Example 5, into an aqueous coagulating bath containing grams per liter of sodium hydroxide and 143 grams per liter of sodium sulfate, and of a pH 13.8. The freshly spun filaments were drawn 100% with rollers and then the alkali adhering to the filaments was neutralized in a neutralizing bath containing 80 grams per liter of sulfuric acid and 300 grams per liter of sodium sulfate. This was followed by submitting the filaments to wet-heat drawing of 100%, then water-washing and thereafter to dry-heat drawing of 200%.

The so obtained filaments had a circular cross-section true to the shape of the spinning hole, and the tenacity of the filaments were 11.8 grams per denier and the resistance to hot water was 119 C.

CONTROLS 7-10 These experiments were operated exactly as in Example 5 except for the conditions indicated in Table II.

agulating bath used was one containing 300 grams per liter of sodium sulfate and grams per liter of ammonia, and of pH 11.8. The resulting filaments had a flat cross-section and their tenacity and resistance to hot water were only 9.3 grams per denier and 102 C., respectively.

EXAMPLE 7 To 1000 grams of 16 weight percent aqueous PVA solution containing 160 grams of PVA of a degree of polymerization of 2350 and a degree of saponification of 99.8 mol percent was added 3.6 grams (2.25 weight percent based on the PVA) of sodium borate, followed by the addition of a minute quantity of hydrochloric acid to adjust the pH of the aqueous solution to 4. This aqueous PVA solution was spun from a spinneret of the same type as used in Example 5, into an aqueous coagulating bath containing grams per liter of sodium hydroxide and 155 grams per liter of sodium sulfate, and of a pH 14. The freshly spun filaments were withdrawn from the bath at a speed of 10 meters per minute, followed by drawing 100% with rollers and neutralizing, after which the filaments were submitted to wet-heat drawing of 200%, water-washing and thereafter dry-heat drawing of 230% to obtain filaments having a total draw ratio of 1900%, whose cross-section was circular, tenacity was 14.5 grams per denier and resistance to hot water was 122 C.

CONTROL 6 Except that the aqueous coagulating bath was one containing 350 grams per liter of sodium sulfate and 250 grams per liter of ammonia, and of a pH 13.5, the experiment was otherwise operated as in Example 7.

The cross-section of the resulting filaments was oval, and their tenacity, resistance to hot water and critical draw ratio were only 9.5 grams per denier, 104 C. and 1100%, respectively.

EXAMPLE 8 To 1000 grams of 14 weight percent aqueous PVA solution containing 140 grams of PVA of a degree of polymerization of 2800 and a degree of saponification of 99.8 mol percent was added 3.5 grams (2.5 weight percent based on the PVA) of boric acid, followed by the addition of a minute quantity of nitric acid to adjust the pH The results were as follows:

In Control 7, due to the slowness of the coagulation speed, undue adhesion between the filaments occurred. The tenacity of the resulting filaments were 10.4 grams per denier, their resistance to hot water was 102 C., and the critical draw ratio was 1350% In Control 8, the spinning was possible on the whole but frequent breakage of the filaments took place. The tenacity of the resulting filaments were 8.6 grams per denier, the resistance to hot water was 102 C. and the critical draw ratio was 1050% In Control 9, due to the coagulation speed being too fast, it was difiicult to apply a draft during spinning of the filaments, and frequent breakage of the filaments were noted. The resulting filaments had a tenacity of 10.6 grams per denier, a resistance to hot water of 105 C. and a critical draw ratio of 1100%.

In Control 10, the spinnability was poor owing to the fact that the dehydration speed at the time of spinning was too slow. While it was possible to form the filaments by retarding the spinning speed to an extreme degree, the filaments thus obtained did not have properties which were worthy of being measured. The critical draw ratio was 1200%.

We claim:

1. A process for producing polyvinyl alcohol filaments of circular cross-section excelling in drawability which comprises spinning from circular spinning holes an aqueous polyvinyl alcohol spinning solution of 10-30 weight percent concentration containing 1-5 weight percent, based on the polyvinyl alcohol, of a water-soluble boric acid compound selected from boric acid, potassium borate, sodium borate, lithium borate and ammonium borate, the pH of said solution being adjusted to 3-5, with a mineral acid into an aqueous coagulating bath containing 20-100 grams per liter of an alkali hydroxide and -180 grams per liter of sodium sulfate, the pH of said bath being adjusted to 13.514.

2. The process of claim 1 wherein said water-soluble boric acid compound is boric acid.

3. The process of claim 1 wherein said alkali hydroxide is sodium hydroxide.

4. The process of claim 1 wherein said alkali hydroxide is potassium hydroxide.

5. A process for producing polyvinyl alcohol filaments of circular cross-section excelling in drawability which comprises spinning from circular spinning holes an aqueous polyvinyl alcohol spinning solution of 14-20 Weight percent concentration containing 2-3 weight percent, based on the polyvinyl alcohol, 01: a Water-soluble boric acid compound selected from boric acid, potassium borate, sodium borate, lithium borate and ammonium borate, the pH of said solution being adjusted to 3-5, with a mineral acid at a temperature of 20-40 C. into an aqueous coagulating bath containing 40-80 grams per liter of an alkali hydroxide and 120-150 grams per liter of sodium sulfate, the pH of said bath being adjusted to 13.5-14.

References Cited UNITED STATES PATENTS 8 3,167,604 1/1965 Arakawa et al. 264-185 3,170,973 2/1965 Tanabe et al 264-485 3,365,527 1/1968 Tanabe et a1 264-185 3,135,648 6/1966 Hawkins 260-29.6 BM 3,438,808 4/1969 Hawkins et al. 260-29.6 BM

FOREIGN PATENTS 166,444 12/1964 U.S.S.R. 264-185 5,822 6/1962; Japan 264-185 JAY H. WOO, Primary Examiner US. Cl. X.R. 

